Concerning the structure for protecting occupant's lower legs, JP, 2000-103367, A and JP, 2000-326870, A disclose inventions, wherein the structure of a vehicle itself is configured to have the desired shock absorption characteristic. Further, JP, 5-330341, A and JP, 6-17097, B, disclose inventions, wherein the foam material that absorbs energy is arranged in foot resting portions in the cabin so as to protect the occupant's lower legs.
However, giving a desired shock absorbent function to the structure of the vehicle itself involves design changes of vehicle body structure and may require additional material and parts to achieve the desired shock absorbent function. So it is predicted to increase the cost.
Moreover, in the case of using a shock absorption material, such as a foam material, since the shock absorption characteristic is fixed, the impact load whose magnitude varies in the deformation process of the vehicle body at the time of a vehicle crash cannot be absorbed effectively.
The energy absorption load of the vehicle in the deformation process at the time of a vehicle crash is highly set up in a rear portion of a front side member rather than in a front portion of the front side member, or is highly set up in an inclined portion that extends from the rear end of the front side member backward and downward along the surface of a toe board of a lower dash panel.
Therefore, the deceleration that acts on the vehicle body becomes suddenly high for a short time interval in the boundary region where the energy absorption load in the rear portion or the inclined portion changes in the direction that becomes high. Then, the rear portion or the inclined portion will deform under the set-up energy absorption load to absorb energy.
In this case, the vehicle after the crash can be stopped by virtue of the high energy absorption load due to the deformation of the rear portion or the inclined portion. At this time, the impact on occupant's lower legs can be reduced by shock absorption material, such as a foam material. However, it is difficult to achieve adequate compatibility between this reduction and the reduction of the impact force which becomes suddenly high for a short time interval in the boundary region at which the energy absorption load of the vehicle body changes.
For the solution to this problem, it is conceivable that by changing the structure of the vehicle body, the energy absorption load difference is made small so as to attain the smooth energy absorption load characteristic. However, this will result in increased manufacturing cost of the body structure.